Beyond Bi-disperse: A study of propensity in a Kob-Andersen Quartet

We simulate the Kob-Andersen bidisperse glassformer system to study dynamics near the glass transition. As the name implies, the standard KA system is composed of two different sized particles. In our system we split the population of large particles into its own binary where half are increased in size and the other half decreased by the same (small) percentage. A similar binary is created for the small particles. Isoconfigurational ensemble runs are then made to understand the influence of slight “errors” in particle size. An isoconfigurational ensemble is a series of simulations, each with the same starting positions but with randomized velocities consistent with the temperature (following Widmer-Cooper et al, 2004). The “propensity” of each particle is defined as the average motion of that particle, averaged over this ensemble. While normally this is done with the exact same particles in the starting positions, having multiple variants of each particle size allows for slight changes to be made to the structure at the start of each run in the isoconfigurational ensemble. We seek to find how large of a change in structure is needed to remove propensity from the system.